Ancient DNA Uncovers 37,000 Years of Human Infectious Diseases

Using ancient DNA extracted from prehistoric remains, a groundbreaking study has uncovered a timeline extending over 37,000 years that details the evolution of human infections. This research, which spans from the frigid mammoth camps of Siberia to medieval burial sites in Denmark, illustrates how pathogens have influenced human history.

The study, led by Eske Willerslev, an evolutionary geneticist affiliated with both the University of Copenhagen and the University of Cambridge, analyzed DNA from 1,313 ancient individuals, revealing genetic traces of 214 distinct pathogens. These pathogens include viruses such as hepatitis B and bacteria responsible for plagues, showcasing a continuous battle between humans and infectious diseases. "We’ve long suspected the transition to farming and animal husbandry opened the door to a new era of disease," remarked Willerslev. "Now DNA shows us it happened at least 6,500 years ago."

The extensive analysis involved sifting through over 400 billion sequencing reads and applying chemical damage patterns to validate which fragments originated from ancient microbes. Remarkably, infections were detected in approximately three-quarters of the skeletons examined, highlighting that illness was a frequent companion throughout human history.

The oldest samples, dating back approximately 37,000 years, primarily contained oral bacteria that are still present today. The findings indicate a significant shift in disease dynamics, coinciding with the advent of agriculture and the domestication of animals around 8,000 years ago. This transition marked an increase in zoonotic pathogens—diseases capable of jumping from animals to humans—evident by the first occurrences of Yersinia pestis, the plague bacterium, around 5,500 years ago in western Russia.

According to the study, a second wave of infections emerged roughly 5,000 years ago, coinciding with the migration of steppe pastoralist groups. These migrations, facilitated by horse-drawn wagons, not only transported people and livestock but also introduced new pathogens to local populations. The resulting waves of infection likely had devastating consequences, leading to ecological changes and potentially paving the way for new settlers.

The researchers noted that the genetic data from ancient infections provides valuable insights for contemporary medicine. Martin Sikora, the lead author, emphasized, "Mutations that were successful in the past are likely to reappear. These ancient genomes can help scientists anticipate future mutations."

The World Health Organization encourages vaccine developers to test candidate antigens against panels of modern strains, making the prehistoric DNA an essential reference point. By comparing pathogen lineages over millennia, researchers can identify which protein targets remain stable and which undergo significant changes. For instance, the ancient plague sequences lack the ymt gene found in modern strains, indicating a historical turning point that transformed local infections into global pandemics.

The skeletal archive also serves as a testament to natural selection, revealing that human alleles associated with inflammatory responses have become more prevalent since the rise of agriculture. While these alleles may have provided protection against livestock-borne infections, they also contribute to the rising incidence of autoimmune disorders in contemporary, cleaner environments.

The research highlights the intricate relationship between infectious diseases and human evolution. As the researchers concluded, "Infectious diseases have left lasting impressions on human genomes, as selective pressures from pathogens have continuously shaped human genetic variation." Understanding the origins, spread, and impact of these ancient pathogens remains a critical and largely unanswered question in the field of human history and genetics.

This significant study was published in the journal Nature, marking a pivotal moment in our understanding of how diseases have shaped human existence over millennia. The implications of this research extend beyond historical curiosity; they offer crucial insights that could inform future public health strategies and genetic research.